By By Mark Leberfinger, AccuWeather.com Staff Writer

October 02, 2014, 7:00:01 AM EDT

Rescue and recovery efforts were halted Monday on Japan's Mount Ontake where 36 people died after the volcano erupted this weekend.

The work by police, firefighters and Japanese Self-Defense Forces was stopped due to high hydrogen sulfide levels on the volcano, Japanese broadcaster NHK reported.

The death toll had been at 31 but NHK reported that five more people were found in "cardiopulmonary arrest" near the summit of the volcano. The Associated Press reported that it is the customary Japanese manner of describing bodies until doctors can examine them.

Twelve people were brought down the mountain and were pronounced dead by a doctor. Twenty-four others remain on the mountain.

The eruption also injured at least 60 people and left 250 climbers trapped initially.

The volcano, 3,097 meters (10,161 feet) high, erupted without warning around 11:53 a.m. Saturday, local time, on the border of the Nagano and Gifu prefectures. It last erupted in 2007. The Asahi Shimbun reported that it is very difficult to predict when such an eruption would occur.

Seven people were rescued from the mountain by helicopter, The AP reported.

The Japanese Meteorological Agency issued a Level 3 volcano alert, urging people to stay away from the area. A 4-kilometer (2.5 miles) area was under the threat of volcanic ash. The volcano was still erupting on Monday.

About 50 centimeters (20 inches) of ash had accumulated near the summit of the volcano, NHK reported. There were also indications of possible pyroclastic flows at the volcano, a scientist told the Asahi Shimbun.